Method of fitting cooperating bodies



June 7, 1927. 1,631,359

c. 5. BROWN METHbD 0F FITTING COQPERKTING BODIES Filed April 18, 1923 7 iviE-W r present invention is clearly Patented June l 7, 1927.

UNITED STATES 4 CHARLES S. BROWN, OF DAYTON, OHIO.

METHOD OF FITTING COOPERATING- BODIES.

Application filed April 18, 1923; Serial No. 632,958.

This invention relates to the art of fitting one body into. a cavity provided by another body and aims to provide an improved method of securing either a press fit or a 5 sliding fit wherein relative movement may take place between the surfaces of the bodies, by means of which it is possible to fit bodies together in a closer relationship than heretofore.

The invention is particularly adapted for fitting a cylindrical body within a cylindrical cavity in another body, and particularly for fitting a piston within an engine cylinder, more closely than heretofore possible without danger of scoring the cylinder during the operation of the engine. I

A further object of the invention is to provide a piston which can be fitted more closely than heretofore possible within the cylinder of an engine, and will automaticall shape itself to conform to the cylinder wal without scoring the cylinder while the engine is running.

A further object is to provide a piston which will tend to remove carbon and other foreign particles from the cylinder walls, and which will tend to conserve lubricating oil while also tending to distribute an adequate supply of oil over the cylinder wall.

Further objects and advantages of the present invention will be apparent from the following description, reference being had to the accompanying drawing, wherein a. preferred embodiment of orlile form of the s own.

In the drawings:

Fig. 1 is a fragmentary view of an air cooled engine certain parts being shown in section to show the construction of a. piston embodying the present invention; and

Fig. 2 is a side view of the piston, one half thereof being shown in section.

'The present invention provides a mode of fitting bodies together which involves providing the surface of one of the bodies with elevated and depressed portions, the elevated portions being initially greater in certain dimensions than the desired surfaces of contact of the body. Then the bodies are placed together and one is moved relative to the other, the surfaces being pressed together, and some of the material is removed from the elevated portions by a shearing, abrading or deforming action, the excess material being collected in the depressed ortions. The elevated surfaces are prefera 1y relat vely narrow in the direction'of the relative motion of the surfaces so that when one body is turned or moved by sliding motion, material will be easily removed from the elevated surfaces rather than front the surface of the other body.

The use of the present invention to fit a piston within -an engine cylinder will first be described. An engine 20 is provided with a crank case 21 supporting a cylinder 22 within whicha piston 23 is adapted to reclprocatet Piston 23 supports a wrist in 30 attached to a. connecting rod'24. In or er to make the piston self-adaptable in size and shape to the interior wall of the engine cylinder, the skirt I of the piston includes portlons engageable with the cylinder wall and capable of being worked down and reduced 1n d 1ameter, andzincludes provisions for receiving the metaLof the distortable portions so as to permit reduction in diameter of the piston. In other words, these provisions receive the surplusimetal which would tend to collect between the cylinder and piston or any other material whichjif allowed to remain along the surfaces of contact would cause the piston to stick within the cylinder and to score the cylinder walls. These material receiving provisions includea plurality of annular grooves 26 provided in the skirt portion 25 of the piston 23. The grooves are spaced relatively close together so as to provide a plurality of relatively narrow annular deformable surfaces 27 for engagement with the cylinder wall. For a 2 inch piston the preferred spacing of the grooves is 4 inch, and the grooves are inch wide 3nd from five to ten thousandths of an inch eep. p

Where an aluminum piston-is used in cooperation with a cast iron cylinder, it has been necessary heretofore to provide a relatively large clearance between the piston.

skirt and the cylinder wall in order that, due to the difference in expansion of the cylinderand piston, the piston will not stick within the cylinder when theengine is heated by its: operation. For example, it has been the practice to provide for an aluminum piston 2 inches in diameter a clearance ranging from seven to nine thousandths of an inch in order that during the operation of the engine some portion of the piston will not bind against the cylinder wall and break the oil film at that point and thus cause the material of the piston to stick or to adhere I to the cylinder walls and to be rubbed between the piston and the cylinder causing both members to be damaged. 1

By theuse of the present invention it is possible to, use only five thousandths of an inch clearance for a 2 inch aluminum piston, when the engine is cold. The engine is operated and the progressiveheating of piston will cause portions of the annular surfaces 27 to bind progressively against the cylinder walls and break the oil film in places. Some of the metal of the piston may be rubbed off from the skirt due to the tendency of the piston to stick but. this metal will be buried over into the grooves to permit the contacting portion of the skirt to be reduced in dimensions so that a neces- VV sary clearance will be automatically obtained to the cylinder walls by the burring over of portions of' the annular surfaces into the grooves 26. Finally the piston wears itself into shape allowing the proper clearance for the oil to be distributed along the cylinder walls. No preliminary lapping of the piston to the cylinder is necessary. The piston will simply shape itself properly while the engine is running.

It has v een observed that the scoring of the cylinder walls results from the surfaces of the piston and cylinder being so close as to break the oil film. Then scoring begins because one surface tends to adhere to the other. Although scoring may tend to take place in an engine constructed in accordance with the present invention, yet the material receiving "grooves 26 receive the material which is removed from the adhering surfaces and therefore the cause for scoring is removed as rapidly as it tends to exist.

The grooves 26 also receive any carbon which may collect on the surfaces 27, and also grit or other forei particles present in the lubricating oil w ich may collect on the walls of the cylinder and would tend to im air lubrication or damage the cylinder wa ls. The carbon collecting in the grooves has a lubricating eifect and therefore the amount of lubricating oil necessary for the pistons can be reduced.

It will also be apparent that the reduction in clearance between the piston and cylinder will result in the reduction of the amount of oil entering between these bodies thereby less noise because of the reduction in piston slap. There will be a reduction in lubricating oil consumption, and there will be less carbon to be removed'from the cylinder walls. g

The present invention is not limited in its application to the fitting of an aluminum piston or to any other piston having a coefiicient ofexpansion greater than that of the material of the cylinder. ,TllB present invention may be applied to fitting a cast iron pistonlwithin an engine cylinder. For example, it has been the practice to'provide from .003 to .005 inch clearance for a 2 inch cast iron piston. By using the present invention the piston clearance can-be reduced' to .002 inch resulting in advantages which have been already described. The

iron piston will tend to expand slightly relative to the iron cylinder owing to a difference in temperature between the piston and cylinder. Therefore the progressive wearing in action is present as in the case of the aluminum piston.

The present invention is not limited in its application to fitting two bodies to pro vide a close sliding fit but is adapted for.

providing a tight press fit. One application of the process to a press fitting operation is shown in Fig. 2. A Wrist pin 30 having a cylindrical bore is provided with plugs 31 terminating at the outer end with a cap or 'button 33. The plug 31 is provided with closely spaced grooves 32 to provide spaced annular contacting .surfaces 3 L The 'external diameter may be a few thousandths larger than the internal diameter of the pin 30. On driving the plug 31 into the wrist pin 30 the excess material at the surfaces 34 will be burred over into the grooves 32. In this manner the plug 31 adapts itself to fit automatically within the pin 30 as the plug is driven into the pin. The plug 31 is preferably constructed of a metal which is softer than the cylinder walls so that should the pin 30 shift axially its ends can not come into contact with the cylinder wall, because of the buttons33 of the Plugs; and at the same time the interior of the cylinder will not be scored, because the said heads or buttons are softer than the material of the cylinder wall.

If any material should be scraped off from the buttons 33 by reason of the contact with cylinder walls it will soon be collected by grooves 26 of the piston.

As explained heretofore, the fitting of two bodies for movement one relativel to the other may take place progressively y gradually expanding one of the bodies relatively to the other.

The clearances between a cylinder and piston greater than 2% inches in diameter will be commensurately greater than the clearances mentioned. For each inch in crease in diameter above 2 inches, the clearance is preferably increased one thousandth of an inch for a cast iron piston. Obviously the clearance for an aluminum piston should be increased by a greater amount. n

While the form of mechanism herein shown and'described constitutes a preferred embodiment of one form of the invention, it is to be understood that other forms might be adopted and various changes and. alterations made in the shape, size, and-\proportion of the elements therein without departing from the spirit and scope of the invention.

What is claimed is as follows:

' 1. The method of fitting two bodies having co-operating surfaceswhich comprises providing one of the bodies with relatively elevated and depressed portions, and moving some of the material of the elevated portions into the depressed portions by producing relative sliding movement between the surfaces while causing the elevated portions of the one body to bear with relatively reat pressure on the surface of the other body.

2.The method of fitting two bodies hav-- ing co-operating surfaces which comprises providing one of the bodies with relatively elevated and depressed portions, and deforming the elevated portions by forcing some of the material thereof into the spaces of the depressed portions by producing relative sliding movement between the surfaces while'causing the elevated portions of the one body to bear with relatively eat pressure on the surface of the other ibdy.

3. The method of fitting two bodies having c'o-operating surfaces which comprises providing one of the bodies with relatively elevatedand depressed portions, and removing material from the elevated portions and collecting it in the depressed portions by producing relative sliding movement between the surfaces while causing the elevated portions of the one bodyto bear with relatively great pressure on the surface of the other body. I

4. The method of fittingtwo bodies having co-operating surfaces which comprises providing one of the bodies with relatively elevated and depressed portions, removing material from the elevated portions and collecting it in the depressed portions by abrasion, and deforming the elevated portions to force some of the material thereof into signature.

ing co-operating surfaces which comprises providing one of the bodies with portions spaced by igrooves, and moving some of the material 0 said portions into the spaces of the grooves by producing relative sliding movement between the surfaces transverse to the grooves while causing the elevated portions of the one body to bear with relatively great pressure on the surface of the other body. 1

6. The method of fitting a cylindrical body withina cylindrical cavity in another body which comprises providing the cylindrical body with a plurality of closely spaced elevated portlonsseparated by grooves, and moving some of the material of the elevated portions into the depressed portions by producing relative sliding movement between the surfaces while causing the elevated portions, of the one body to bear with relatively great pressure on the surface of the other body.

7. The method of fitting two bodies hav-- elevated and depressed portions and gradually moving someof the material of the elevated portions into the depressed portions by producing relative sliding movement between the surfaces while thermally changing the size of one of the bodies to gradually increase the pressure between the elevated portions of one body and the surface of the other body.

9. The method of fitting a piston within the cylinder of a machine inherently adapted to develop heat during operation which comprises providing the piston with relatively elevated and depressed portions, the

elevated portions fitting tightly within the,

cylinder, and moving some of the material of the elevated portlons of the piston into the spacesof the depressed portions by operation of the machine.

In testimony whereof I hereunto aifix my CHARLES S. BROWN. 

